Tuberculosis (TB) is caused by the Mycobacterium tuberculosis complex (MTB-complex) and usually attacks the lungs and many people carry the MTB-complex bacteria without ever developing active disease.

Current TB infection control guidelines recommend placing a patient suspected of having active TB in an airborne infection isolation room and keeping that person isolated until clinical and laboratory information, including acid-fast bacilli (AFB) smear testing of three sputum specimens, each collected eight to 24 hours apart show that the patient is unlikely to have contagious TB.

The US Food and Drug Administration (FDA; Silver Springs, MD, USA) has cleared a molecular assay that helps physicians determine if patients with suspected TB can be removed from airborne infection isolation. This expanded use allows healthcare providers to use one or two negative assay test results to help them determine whether a patient showing signs and symptoms of pulmonary TB should continue to be kept in a hospital airborne isolation room.

The Xpert MTB/RIF Assay (Cepheid, Sunnyvale, CA, USA) is a nucleic acid amplification test, different from a smear in that it can test specifically for the DNA of the mycobacteria that cause TB. This test can detect TB better than the smear test, and can detect TB even when the smear test may be negative. Because the MTB/RIF test can detect TB better than the smear, results from one or two MTB/RIF tests can be used in the decision to remove patients from isolation. A single negative MTB/RIF test result predicted the absence of MTB-complex on AFB smears 99.7% of the time, and two consecutive negative MTB/RIF test results predicted the absence of the bacteria 100% of the time.

Philip LoBue, MD., director of the Center for Disease Control’s Division of Tuberculosis Elimination (CDC; Atlanta, GA, USA) said, “We are encouraged that a quicker option for detecting contagious TB is now available to assist in determining whether patients must remain in isolation. The test may make it possible for some patients to be released from hospital isolation sooner, freeing up limited medical resources and removing restrictions on patients’ movements and interactions. While this test can assist health care providers in making important decisions regarding isolation, it does not replace the continued need for culture testing to ensure patients with TB are accurately diagnosed and treated.”

Related Links:
US Food and Drug Administration 
Cepheid
CDC